The present invention relates to a method and a device for determining a gas charge of an internal combustion engine. The invention is applicable in particular to the field of automotive engineering, for example, in an internal combustion engine in a passenger car.
Customary internal combustion engines have an intake manifold in which a gas mixture made up of a fresh air/fuel mixture and an exhaust gas is located. During the operation of the internal combustion engine, this gas mixture is drawn into the cylinder volume of the internal combustion engine and subsequently compressed and burned. The volume of the gas flowing into the cylinder, in particular the fresh air/fuel mixture component of this volume, must be determined to meter the quantity of fuel to be made available for combustion.
German Patent No. 32 38 190 concerns an electronic system to control or regulate the operating characteristics of an internal combustion engine. In doing so, the pressure in the intake manifold is determined based on speed and air throughput in the intake manifold and/or the air throughput is determined based on speed and pressure.
German Paten Application No. 1 97 13 379 concerns a device for determining the air entering the cylinders of an internal combustion engine having a supercharger. This system also takes into account the physical circumstances additionally occurring due to the supercharging. In particular, the physical events occurring in the intake manifold of an internal combustion engine with a supercharger can be readily detected by including physical and fluid engineering relationships.
At least some methods and devices treat the gas mixture present in the intake manifold uniformly with regard to the determination of the gas charge of the internal combustion engine. In particular, no distinction is made between a fresh air/fuel mixture component and an exhaust gas component in the gas mixture. As a result of this, the determined gas charge volumes contain errors. The non-linear relationship between the measured quantities and the target variable of charge per stroke as well as the influence of exhaust gas recirculation are corrected directly in an empirical manner. Such a correction is only precise in a steady-state condition. Moreover, the variable relationship between the gas charge and the intake manifold pressure such as occurs, for example, with active tank ventilation or cam adjustment is not taken into account.
An object of the invention is therefore to provide a method and a device for determining a gas charge of an internal combustion engine which overcomes the disadvantages described above. In particular, the object may be achieved by determining the fresh air/fuel mixture component in the charged gas volume. Moreover, the invention should be very flexible with regard to the input variables used. In addition, the method according to the invention should be robust and reliable in operation and the associated device should be economical to produce, operate and maintain invention are described in the sub-claims.
A listing of the abbreviations used in the following description can be found at the end of the description.
The aforementioned objects may be achieved by a method for determining a gas charge of an internal combustion engine having an intake manifold, a gas mixture made up of a fresh air/fuel mixture and an exhaust gas being present in the intake manifold, a gas mass flow mp_ab flowing out of the intake manifold and an intake manifold pressure (ps) being present in the intake manifold, including by the steps: determining of a partial pressure of fresh air/fuel mixture component ps_fg in gas mass flow mp_ab by setting up a mass balance for a fresh air/fuel mixture mass flow mp_fg and determining of a partial pressure of exhaust gas component ps_ag in gas mass flow mp_ab by setting up a mass balance for an exhaust gas mass flow mp_ag. In setting up the mass balance, the time derivation of the general gas equation
mxc3x97Rxc3x97T=pxc3x97V
is to be understood in particular. Accordingly, the mass balance for the fresh air/fuel mixture component is as follows:                     mp_fg        =                                            mp_fg              ⁢              _zu              ⁢              _                        -                          mp_fg              ⁢              _ab                                =                      xe2x80x83                    ⁢                                    ⅆ                              ⅆ                t                                      ⁢                          (              m_fg              )                                                              =                  xe2x80x83                ⁢                              ⅆ                          ⅆ              t                                ⁢                      (                          ps_fg              xc3x97              VS              xc3x97                              1                                  R                  xc3x97                  TS                                                      )                              
Correspondingly, the following applies to the mass balance for the exhaust gas component:                     mp_ag        =                                            mp_ag              ⁢              _zu                        -                          mp_ag              ⁢              _ab                                =                      xe2x80x83                    ⁢                                    ⅆ                              ⅆ                t                                      ⁢                          (              m_ag              )                                                              =                  xe2x80x83                ⁢                              ⅆ                          ⅆ              t                                ⁢                      (                          ps_ag              xc3x97              VS              xc3x97                              1                                  R                  xc3x97                  TS                                                      )                              
This separate balancing of fresh air/fuel mixture and exhaust gas offers the advantage that the charged fresh air/fuel mixture volume can be calculated precisely. This advantageously makes an exact and reliable determination of the quantity of fuel to be supplied possible. It makes environmentally acceptable and energy-saving operation of the internal combustion engine possible. As a result, the operating costs of the internal combustion engine are reduced and its life expectancy is increased. Moreover, it is advantageous that a precise determination of the quantity of fuel to be supplied is made possible even with various configurations of the internal combustion engine, for example, with or without exhaust gas recirculation, with or without supercharging, etc.
In an exemplary particular embodiment of the invention, the method calculates intake manifold pressure ps from the sum of the partial pressure of fresh air/fuel mixture component ps_fg and of the partial pressure of exhaust gas component ps_ag. This calculation is made via the addition:
Ps=Ps_fg+ps_ag
This calculation of intake manifold pressure ps offers the advantage that a possibly additionally measured value for the intake manifold pressure can be checked using the calculated value. Moreover, it is an advantage that the intake manifold pressure can be determined in this manner without the additional expense of a pressure measuring sensor. In addition, it is advantageous that the intake manifold pressure can be determined in this manner even in the event of failure of an existing pressure measuring sensor.
An exemplary embodiment of the invention determines intake manifold pressure ps using a corresponding measuring sensor. Any commercially available pressure measuring sensors may be used as measuring sensors, wire strain gauges, diaphragm pressure sensors or resonant pressure sensors, in particular. The pressure may be determined directly or indirectly via an intermediate medium. The signal supplied by the pressure measuring sensor may be additionally processed by appropriate circuitry; for example, a temperature compensation or an offset balancing may be provided. The determination of intake manifold pressure ps using a measuring sensor offers the advantage that intake manifold pressure ps can be determined very precisely with it. Moreover, it is an advantage that the intake manifold pressure calculated via the partial pressures can be checked and corrected if necessary and the calculation can be calibrated via the measured intake manifold pressure.
An exemplary embodiment of the invention determines gas mass flow mp_ab from the intake manifold pressure. This determination is made with the consideration of speed n of the internal combustion engine as well as a camshaft adjustment NWS that may be present in the internal combustion engine from which a correction value p_iagr of the internal exhaust gas recirculation is taken into account. In particular, this makes it possible to determine gas mass flow mp_ab flowing out of the intake manifold according to the equation:
mp_ab=(psxe2x88x92p_iagr)xc3x97K.
The value K in this connection is a calculation constant in which the pump equation is included and possible pulsation effects that were determined empirically are included. The advantage of this calculation of the gas mass flow mp_ab is that it is possible even without the provision of a measured intake manifold pressure, solely on the basis of the calculated partial pressures. This makes an economical and reliable implementation of the method according to the invention possible.
In an exemplary embodiment of the invention, fresh air/fuel mixture component mp_fg_ab in gas mass flow mp_ab flowing out of the intake manifold is calculated using the partial pressure of fresh air/fuel mixture component ps_fg, the partial pressure of exhaust gas component ps_ag and gas mass flow mp_ab. For this purpose, a proportional factor c_agr is initially introduced which is calculated as follows:   c_agr  =      ps_ag          ps_ag      +      ps_fg      
In order to determine the fresh air/fuel mixture component in this mass flow, it is assumed that the distribution of the mass flows into the cylinder (fresh air/fuel mixture and exhaust gas) takes place by analogy to the distribution of the partial pressures. Accordingly, fresh air/fuel mass flow mp_fg_ab flowing out of the intake manifold is calculated as:
mp_fg_ab=(1xe2x88x92c_agr)xc3x97mp_ab
Correspondingly, the following applies to exhaust gas mass flow mp_ag_ab flowing out of the intake manifold:
mp_ag_ab=(1xe2x88x92c_agr)xc3x97mp_ab
It is advantageous that as a result of this simple and reliable calculation, it is possible to determine both the fresh air/fuel mixture component as well as the exhaust gas component in the gas mass flow flowing out of the intake manifold. The separate detection of the fresh air/fuel mixture and exhaust gas component makes environmentally acceptable and energy-saving operation of the internal combustion engine possible in its particular optimum operating point.
In an exemplary embodiment of the invention, relative fresh air/fuel mixture charge rl of the internal combustion engine is calculated using fresh air/fuel mixture component mp_fg_ab as well as permanent MLTHZ and transient nmot, ZYLZA engine data. The advantage of the calculation of relative fresh air/fuel mixture charge rl is that the fuel can always be supplied based on current engine data, for example, based on the number of active cylinders of the engine in operation at the moment. This further increases the effect of fuel economy and environmental compatibility during operation of the internal combustion engine as well as further improves its life expectancy and performance.
In an exemplary embodiment of the invention, a function derived from the Bernoulli equation is used for the calculation of a gas mass flow via a throttle, the pressure downstream of the throttle always corresponding to intake manifold pressure ps. This has the advantage that optionally some of the measured quantities that are suitable in principle can be used and the variables that are not available in each case can be calculated via this derived function. This allows for great flexibility of the method according to an exemplary embodiment of the invention both in the implementation of the method in the form of a device as well as during the operation of such a method. In addition, this flexibility of the configuration also increases the operational reliability of the method according to an exemplary embodiment of the invention.
In an exemplary embodiment of the invention, gas flows via an idle actuator mp_lls, gas flows via a fuel-tank venting valve mp_tev, gas flows via an exhaust gas recirculation valve mp_agr and also charge-air pressure pld in a supercharged internal combustion engine are also taken into consideration in determinating the gas charge of the internal combustion engine. The advantage of this is that the precision of the determined fresh air/fuel mixture charge of the internal combustion engine is further increased and consequently the aforementioned advantages are increased.
A exemplary embodiment of the present invention also includes a device for determining a gas charge of an internal combustion engine having an intake manifold, the device having measuring sensors and an electronic means of computation which calculates a partial pressure of a fresh air/fuel mixture component ps_fg in the intake manifold by setting up a mass balance for a fresh air/fuel mixture mass flow mp_fg, calculates a partial pressure of an exhaust gas component ps_ab in the intake manifold by setting up a mass balance for an exhaust gas mass flow mp_ab and determines a fresh air/fuel mixture charge rl of the internal combustion engine using the partial pressure of fresh air/fuel mixture component ps_fg and the partial pressure of exhaust gas component ps_ab. In particular, the invention includes a device which implements a method as described above. This device according to an exemplary embodiment of the invention offers all the advantages that have already been named above for the method according to an exemplary embodiment of the invention. In particular the device offers the advantage of low fuel consumption, an environmentally compatible operation of the internal combustion engine as well as high performance and a long life of the device and of the internal combustion engine.
An exemplary embodiment of the invention also includes a motor vehicle having a device as described above and/or a motor vehicle having a device which can implement a method as described above. The advantages named above for the device according to an exemplary embodiment of the invention also apply to the motor vehicle correspondingly.
An exemplary embodiment of the invention also includes a data medium containing a control program for implementing the above-described method as well as a data medium containing parameters which are necessary or advantageous for implementing such a method and/or for the control of a device described above. In particular, such a data medium may be designed in the form of a storage medium in which the storage can take place mechanically, optically, magnetically, electronically or by other means. Electronic storage media in particular, such as for example, ROM (Read Only Memory), PROM, EPROM or EEPROM, that may be used and/or inserted in corresponding control devices, may be used.
Additional advantages, features and details of the exemplary embodiments of the present inventions may be realized with respect to the following description, including the Figures, of the exemplary embodiments of the present inventions.